Many oil reservoirs, such as heavy oil or tar sand formations, exist which contain vast quantities of oil which cannot be recovered by conventional techniques because the oil is so viscous that it is substantially immobile at reservoir conditions. Therefore, some form of supplemental oil recovery must be used in such formations to decrease the viscosity of the oil sufficiently to allow it to flow through the formation to the production well and then be brought to the surface of the earth. Thermal recovery techniques which decrease the viscosity of such oil and are therefore suitable for stimulating the recovery thereof include steam flooding and in-situ combustion. Because steam is generally the most economical and efficient thermal energy agent, it is clearly the most widely employed.
A thermal recovery process wherein steam flooding is utilized to remove viscous oil from a formation is described in U.S. Pat. No. 4,456,066 to Shu. In another thermal recovery process described in U.S. Pat. No. 4,565,249 to Pebdani et al., a mixture of carbon dioxide and steam is injected into a viscous oil-containing formation. In yet thermal recovery process described in U.S. Pat. No. 4,961,467 to Pebdani, both steam injection and in-situ combustion are utilized in producing a viscous oil-containing formation.
Production wells penetrating subsurface oil-bearing formations utilize perforations in well casing through which formation fluids enter the well. Such oil production wells often penetrate viscous oil-bearing formations. Fines and particles, such as sand, are often entrained in the viscous oil produced from such formations. Because the oils are viscous, conventional gravel pack techniques cannot be used to remove the fines when the viscous oil is produced. Utilization of conventional gravel packs would greatly impede the flow of the viscous oils therethrough and would result in a loss of production. For this reason, these viscous oils are produced to the surface with the fines entrained therein. Once on the surface, the fines are removed from the oil and disposed of.
However, not all the fines entering the production well entrained in the viscous oil will be transported to the surface of the earth. Some of these fines will settle out of the fluid flow up the well and can eventually build up to the point of inhibiting fluid flow and causing shut-down of the well's pump.
It is therefore a specific object of the present invention to provide well apparatus for fluidizing such formation fines within the well so as to prevent their settling and to insure their production through the well pump to the surface of the earth for disposal.